Rate measuring device



Dec. 22, 1942.

A. A. STUART, JR

RATE MEASURING DEVICE Filed Oct. 3, 1942 3 Sheets-Sheet 1 ILOADI l4 PhaseA T0 ENG/NE lg W 2/ 22 I2 \dW-E Phase 6 Phase 0 7'0 ENG/NE INVENTOR.

ATTORNEY.

ec. 22, 1942. A, A. STUART, JR

RATE MEASURING DEVICE Filed 001:. 3. 1942 3 Sheets-Sheet 2 I LOAD I INVENTOR.

/f'red A. Sfu J" ATTORN EY.

Dec. 22, 1942. A. A. STUART, JR 2,306,361

RATE MEASURING DEVICE Filed Oct. 3, 1942 3 Sheets-Sheet 3 Phase C INVENTOR.

ATTORN EY.

atented RATE MEASURING IIDEWCE Alfred A. Stuart, .ln, Hasbrouck Heights, N. 3.,

assig'nor to Bendix Aviation Corporation, Bendin, N. .lL, a corporation of Delaware Uriginal application March 27, 1941, Serial No. 385,577. Divided and this application October 3, 1942, Serial No. 460,673

3 Claims.

The present invention relates to rate measuring devices of a type which may be readily adapted to the measurement of rotative speeds, and is a division of copending application Serial No. 385,577, filed March 27, 1941.

It is an object of the present invention to provide a shaft tachometer, wherein the speed of the shaft may be measured by displacement of the phase of one voltage source with respect to the phase of another voltage source.

Another object of the invention lies in the provision of a shaft tachometer wherein the phase of the voltage of one source may be shifted with respect to the phase of the voltage of another source in accordance with the speed of a driving shaft.

Other objects include the provision of a rate indicating device wherein the indicating element may be a self-synchronous motor or a cathode ray beam tube of novel construction, and the provision of a tachometer particularly adapted for giving remote indications of shaft speed.

Another object of the invention is to provide a novel shaft tachometer wherein the phase of the voltage of one source is shifted with respect to the phase of another source, either mechanically by a resilient coupling or electrically by a phase-shifting network, in accordance with the speed of a driving shaft, and wherein the indicating element is of the-electronic type such as a cathode ray tube, for example.

Other objects will appear from a study of the following specification when made in conjunction with the attached drawings, throughout which like numerals designate like parts.

Fig. 1 is a schematic diagram of one form of the invention;

Fig. 2 is a diagram of a second embodiment of the invention;

Fig. 3 is a diagrammatic representation of a generators of alternating current are driven by a shaft, the speed of which it is intended to measwe and a phase-shifting device is provided for shifting the phase of the voltage of one generator with respect to the voltage of the other in accordance with the rotative speed of the driving shaft.

One of the generators may be polyphase while the other is single phase. The phase-shifting device may be either mechanical or electrical, and the indicating device may be a polyphase electric motor or a cathode ray tube,,with a cathode ray beam functioning as a pointer to indicate the rotative speed of the driving shaft.

Having particular reference to Fig. 1, Ill represents a polyphase alternator having a rotor II, which may be a permanent magnet of Alnico or of any other suitable material, carried on a shaft I2 supported in a bearing member I3, which is schematically shown. Alternator ID has a stator portion, which includes a phase winding I l designated as phase A, and a phase winding I5 designated as phase B at 90 degrees to phase A. A single phase alternator I6 has a rotor ll, which may be a magnet of Alnico," or other suitable material, and a stator including a phase winding I8, designated as phase C. Rotor II is carried by a shaft I9 journaled in bearing members 20 and 2i, which are schematically shown. Shaft I9 is coupled by any suitable means to the shaft of the engine, not shown, the speed of which it is intended to measure. A spring member 22 is interposed between shafts I2 and I9, and while it is schematically represented, it may be a spiral, a leaf spring or any other conventional type of spring.

An indicating member includes a polvphase motor 23, having stator windings 2t and 25 connected in series with phase A, and stator windings 26 and 21, connected in series with phase B. A rotor member 28 which carries a pointer 29, is connected to the single phase winding I8 of alternator It. Motor 23 may be of the self-synchronous type known as an Autosyn or Selsyn," wherein the position of the rotor with respect to the stator will depend on the phase relation between the voltages in the stator and in the rotor. A scale member 30, which may be circular, but which is shown broken away, coacts with pointer 29 in order to give an indication of the rotative speed of the engine shaft.

Spring member 22 is designed so that upon rotation of shaft l9 by the engine, shaft I2 will be carried along with shaft I9, but at a phase displacement which varies with the torque imposed upon spring 22.

Ordinarily the torque developed in a generator varies substantially in accordance with the speed of rotation of the armature, but in order to insure that the torque vary directly with the speed of rotation, an impedance load HI is placed across the output of winding It and a similar impedance load I5 is placed across the output of winding I 5. The proper relation of impedances that make up loads It and I5 may be selected for any given generator Ill so that the desired torque-speed relation will be maintained. A workman skilled in the art will be capable of ascertaining the right value for loads l4 and I5 and further explanation thereof is accordingly believed to be unnecessary.

As equal increments of speed of the engine shaft bring about equal increments of the torque thereof, it will be seen that the physical phase relation of rotors II and I! will be varied in accordance with the speed of the engine shaft, thus the voltages generated in phases A and B will lag the voltage generated in phase C by an amount that varies with the speed of rotation of the engine shaft. The phase displacement by which the voltages in alternator l lag behind the voltage generated in alternator I is indicated by pointer 29 directly as R. P. M. on scale 30, if desired, since rotor 28 which carried pointer 29,

will take up an angular position with respect to the stator of alternator l0 which depends on the speed of the engine shaft.

Phase C need have no particular initial phase relation to phases A and B, since regardless of the initial relation, it will be altered in the same manner as shaft I9 is rotated, but if desired, phase C may be in phase agreement with either of phases A or B when generators l5 and I5 are at rest.

The phase shift which indicates a change in engine speed may be brought about by an electrical, rather than a mechanical, phase shifting means, and in Fig. 2 rotors II and H, of alternators l5 and I5, are rigidly connected to the engine-engaging shaft l9 and are preferably so aligned mechanically that there is zero mechanical phase displacement between identical points of each of the rotors secured to shaft IS. The output of phase l5 connects to the input of a phase shifting network 9| which may include any conventional electrical network system; for example, one comprising condensers 32 and resistors 33.

Whenever, in a given network, such as that shown at 31, the input frequency changes, a shift in the phase of the voltages applied will be brought about so that the voltage in the output of the phase shifting network will bear a definite phase relation to the voltage in the input thereof,

and this phase relation will vary with the frequency of the input voltage. By using capacitances and resistors, having certain related values as will be understood by those skilled in the art, it is possible to shift the phase of the voltage from phase 0 in a linear relation with respect to the voltages generated in phases A and B, and as the angular speed of shaft I9 varies, the frequency shift of voltage in phase C varies accordingly.

Since phase shifting network 3| operates to linearly shift the phase of the voltage in stator It! with respect to the speed of shaft l9, the phase of the voltage will be accordingly shifted by the same amount in rotor 29, and it will be apparent that pointer 29 will be rotated so that it indicates theamount of phase shift brought about for a given speed of rotation of shaft l9.

The novel tachometer herein disclosed may utilize a unique type of indicator, shownparticularly in Figs. 3 and 4. This indicator is a thermionic'vacuum tube of the type disclosed and claimed in U. S. Patent No. 2,283,103 dated May 12, 1942, and assigned to the same assignee as the present invention. This cathode ray tube is shown only schematically in Figs. 3 and 4, but it is believed its operation will be clear upon an explanation thereof.

A cathode ray vacuum tube 34 includes an annular anode member 35 coated with any suitable fluorescent material and having a central aperture 36. Within this aperture and coaxially of anode 35, there is positioned a cathode member 31 which may be of any conventional type, such as an indirectly heated cathode, and surrounding cathode 3'! there is positioned a cylindrical Wire mesh control grid member 38. Immediately outside control grid 38 and symmetrically spaced about cathode 31 within aperture 36 there are located four director electrode members 39, 40, 4| and 42, which may be short rods of small diameter, running parallel to the axis of anode 35. By means of leads 43 and 44, which are connected to opposite director electrodes 39 and 4|, respectively, these electrodes are electrically connected in circuit with phase A through the transformer 45. Similarly, director electrodes 40 and 42 connect to leads 4G and 41, respectively, and are attached in circuit with phase B by means of transformer 48. It will be seen therefore, that director electrodes 39 and 4| are connected electrically degrees out of phase with respect to director electrodes 40 and 42. Phase winding Ill, which is phase C of alternator I6, is connected to the primary 49 of a transformer 50, having a secondary winding 5| center tapped and grounded at point 52.

When alternator I5 is in operation (that is, when rotating shaft l9 carries rotor l1), an alternating current, the frequency of which depends upon the speed of rotation of shaft I9, is generated. The energy generated is transformed, in transformer 50, into suitable voltage and current values to operate tube 34. The alternating current in the output of transformer 5|) is rectified by means of a rectifying system 53 which will be now described. Diode 55 rectifles and passes positive half-cycles of energy from transformer 55, as indicated by the plus sign, and has a conventional filter condenser 51 connected to ground across its output. A bleeder resistor 51' is shunted across condenser 51 for the conventional purpose of discharging condenser 51, and thus preventing the accumulation of a high charge across condenser 51. The rectified voltage in the output of diode 55 is impressed upon anode 35 through lead 58. This voltage is of course positive and will be of the value desirable for the best operation of tube 34.

The diode 54 also rectifies the voltage in the output of transformer 59, but it is so poled with respect to diode 55 that it passes only negative half cycles of alternating current. A conventional filter condenser 55 is connected to round across the output of diode 54 and a conventional bleeder resistor 55' is shunted across condenser 55 to prevent the accumulation of a high charge on condenser 56. A negative voltage of any suitable value is impressed upon director electrodes 39, 49, 4| and 42 through lead 59, center taps 55 and 5|, and the secondaries of transformers 45 and 48, respectively. Further, a negative bias of a value suflicient to maintain control grid 38 in its cut-off condition is impressed by diode 54 by Way of lead 59, secondary winding 63 and conductor 52.

The negative bias impressed upon control electrodes 39, 49, 4|, and 42 is of such value that when it is combined with the signal voltages on these electrodes due to phase windings A and B of generator l9, emission of electrons from cathode 31 to anode 35 is restricted to a narrow beam 55, which will revolve synchronously with rotor Ill of alternator l3. Although the description herein is believed to be complete so that one skilled in the art may construct the invention in accordance with this disclosure, a detailed explanation of the operation of the novel cathode ray tube is contained in Patent No. 2,283,103 above-mentioned.

synchronously revolving beam 65 cannot be read in motion as an indication of rotative speed, and therefore rectifier 53 is made to impress a normal negative bias upon anode 35, which bias of control grid 38 is removed for an instant in each revolution of shaft H3 at a particular angular position with respect to scale 30. This position depends upon the phase displacement be-- tween the rotors Ill and ll, and at this instant, beam 65 is formed on anode 35 by the action of electrodes 39, 33, M and 32. The means employed for instantaneously removing the negative bias of grid 33 includes a pulsing circuit comprising a thermionic device 66 of the pentode type which has its control grid 61 connected across phase winding l8 of alternator It. This pentode has the usual cathode member 68 which is shown conventionally grounded to one side of phase winding l8.- Cathode 68 may be of the indirectly heated type, and a battery or other source, not shown, may be utilized to heat cathode 33 to its emitting condition. An additional grid or control member 63, ordinarily called the screen grid, is connected to the positive output of rectifier diode 55 by means of conductors l0 and 58 and the conventional suppressor grid 69' is connected to cathode 68. Anode potential is provided for the anode H through the primary winding M of transformer 63.

It is characteristic of the pentode type of tube such as the SL6, that its anode-cathode, or output, circuit will contain a current, the amount of which is controlled by the voltage on the control grid, but as this voltage is made negative beyond a certain definite point, the current in the output circuit is stopped or materially decreased at an exceedingly high rate for a minute change in grid voltage. When the grid voltage is cyclicly changed, as in the instant case, then this characteristic point will occur at the same point of the sine wave of voltage from alternator it once during each cycle, and the grid 61 will cut ofi the output current at the same high rate. The constant recurrence of this cut-off point once during each cycle affords a means whereby beam 35 is allowed to fluoresce or form on anode 35 in each cycle for the brief instant of cut oil of the anode-cathode current flowing through the primary 12 of transformer 63.

It is fundamental that when a current is stopped through a circuit including an inductance, a short pulse or surge of voltage occurs during the instant that the current is stopped, and if the inductance is relatively high, the pulse or surge reaches a peak voltage many times the voltage of the exciting source. The value of this peak depends principally on the amount of inductance in the circuit and the rate at which the current is stopped. As an example, it has been found that using a 6L6 type pentode, the rate at which the anode-cathode current is cut off by" control grid til is such that, with only 12 volts on anode 1H and an inductance in primary 72 of 800 henrys, a pulse or surge of 120 volts (positive) is induced in the secondary B3 and impressed on control grid 33. The normal bias on control grid 33 suflicient to maintain beam 65 cut-on may be on the order of minus so volts,

and it will be seen that for the brief instant that the pulse or surge of 120 volts exists, electrode 38 loses control and beam 65 fluoresces on anode 35 under the influence of director electrodes 33, 40, 4H and 32. Due to the persistence of the screen formed by the fluorescent material on anode 35 and to the persistence of vision, beam 65 will appear to be continuously on, and when the speed of shaft I9 is constant, beam 65 will appear to be stationary. When'the shaft I9 is accelerating, pointer or beam 65 will appear to move in accordance with the rate of acceleration, in the same manner that the conventional mechanical pointer moves when the speed of the shaft or vehicle under observation changes.

The embodiment of the invention shown in Fig. 4 varies from that shown in Fig. 3 only by the use of the electrical phase shifting network 3|, which is substituted for the spring member 22. The operation of phase shifter 3| is fully explained above in the description of Fig. 2 and since the operation of the pulsing tube 86 and the cathode ray tube 34 have been described in conjunction with the description of Fig. 3, it is believed that the operation of the embodiment shown in Fig. 4 will be readily understood.

The phase shifting network 3| is shown as being composed of resistances 33 and capacitances 32, but it will be understood that many impedance combinations of inductances and resistors, or inductances, capacitances and resistors may be employed. Further, it is obvious that rotor ll of alternator II) in Figs. 1 and 3 need not lag behind rotor ll of alternator it, as either rotor may be made to lead without changing the concept of the invention. While the rotors H and I! have been shown as permanent magnets, they may be electromagnets if this seems preferable for certain uses of the present invention.

The loads l4 and [5' shown in Figs. 1 and 3 are electrical in character, but a mechanical load, such as a brake applying a drag to shaft l2 may be used instead, as will be readily appreciated.

The rate measuring instrument of the present invention may be used rather generally, but it is particularly well adapted to use on ships and in aircraft, where the engines under observation are at a considerable distance from the pilot's or navigators station, since no flexible mechanical shafting is utilized to transfer indications. Flexible shafting is not only bulky and unwieldy for use over long distances but it also has inherent angular errors and adds considerable weight to the instrument. An added advantage of the present invention is that any number of repeater indications may be provided at different stations by merely placing a plurality of Autosyns" 23 or cathode ray tubes 34 in parallel.

It will be understood that many changes, not herein specifically treated, may be made to the embodiments shown, without the exercise of invention. The invention is to be limited, therefore, not by the forms shown and described, but by the scope of the appended claims.

I claim:

1. A shaft tachometer comprising a first alternator having a rotor driven by said shaft and a stator, a second alternator having a rotor driven by said shaft and a polyphase stator, a cathode ray indicating device including an anode, means for impressing a positive potential thereon, an electron-emissive cathode, a plurality of control electrodes symmetrically spaced about said cathode, means for impressing a negative potential on said control electrodes, connections between said polyphase stator and said electrodes, a control grid, means for shifting the phase of the voltage of said first alternator with respect to the phases of voltages of said second alternator, and means in circuit with said control grid and said first alternator for limiting the interval of emission from said cathode to said anode to a unique point in each cycle of rotation of said shaft.

2. A device for indicating quantities representative of an operating condition of a shaft, comprising a first alternator having a shaftdriven rotor and a stator, a second alternator having a shaft-driven rotor and a stator, said rotors having a fixed angular phase relation when at rest, means interposed between said rotors to vary said angular phase relation in accordance with the speed of said shaft, a thermionic indicating device including an annular anode coated with fluorescent material, an electron-emissive cathode, a plurality of symmetrically spaced director electrodes about said cathode, a control grid electrode surrounding said cathode, symmetrical connections between the stator of one of said alternators and said director electrodes, a source f anode potential, the input of an electrical pulsgng circuit connected to the stator of the other pf said alternators, and a connection between the output of said pulsing circuit and said control grid electrode whereby emission of electrons aaoaaci from said cathode to said anode is restricted to a brief interval of a cycle of rotation of said shaft-driven rotors.

3. A device for indicating quantities representative of an operating condition of a shaft, including a first alternator having a stator and a shaft-driven rotor, a second alternator having a stator and a shaft-driven rotor, a cathode ray beam device including a sealed envelope, an annular anode coated with fluorescent material, a central cathode of electron-emissive material, a plurality of director electrodes spaced about said cathode in symmetrical arrangement, a control grid surrounding said cathode, symmetrical connections between said director electrodes and the stator of said first alternator, a pulsing circuit having its input energized by a circuit including the stator of said second alternator, its output connected to said control grid, and means for shifting the phase of the voltage from said second alternator with respect to the voltage from said first alternator in accordance with the speed of said shaft, said pulsing circuit acting to prevent electrons emitted from said cathode from forming a beam on said anode except for a brief interval in each cycle voltage from said second alternator, the occurrence of said interval varying withthe phase-shift in voltage from said second alternator.

ALFRED A. STUART, Ja. 

